Operation
Climate Control OperationThe climate control system is a manual system which heats or cools the vehicle depending on the function selector switch position and the temperature selected.
The function selector switch is a vacuum and electrical switch that controls the A/C compressor and air distribution.
- The temperature control switch is a cable operated system that controls the air temperature door.
- The heater blower motor switch varies the blower motor speed.
Electrical Component:
1. Climate control panel
2. A/C cycling switch
3. Dual pressure switch
4. Powertrain control module
5. A/C relay
6. A/C clutch field coil
7. Heater blower motor resistor
8. Blower relay
9. Blower motor
10. Fan motor
System Air Flow Description
When MAX A/C is selected:
- The air inlet blend door is at full vacuum, closing off outside air and allowing only recirculated air.
- The defrost blend door is at full vacuum while the footwell blend door is at no vacuum, closing both doors.
- The vent/register blend door is at partial vacuum, directing airflow to the driver-side, passenger-side and center registers.
- Temperature control is usually set for maximum cold but may be heated if selected.
- Air is picked up at the recirculation opening by the blower motor. With the temperature control set for maximum cold, air flows across the A/C evaporator core, diverting past the heater core and then directed into the passenger compartment through the driver-side, passenger-side and center registers.
- The A/C compressor is enabled when MAX A/C is selected.
- The blower motor is on.
When A/C is selected:
- The air inlet blend door is set at no vacuum, blocking the recirculation passage and admitting outside air.
- All other door positions are the same as described under MAX A/C.
- Temperature setting can be changed manually.
- The A/C compressor is enabled when A/C is selected.
- The blower motor is on.
When panel is selected:
- The air inlet blend door, with no vacuum being applied, blocks recirculated air and allows outside air. Air flows through the system to the driver, passenger and center registers.
- The vent/register blend door is at partial vacuum to direct airflow to the driver, passenger and center registers.
- The defrost blend is at full vacuum and defrost airflow door is at no vacuum, closing off airflow to the windshield defroster hose nozzles and footwell ducts.
- The temperature setting can be changed manually to heat the air but air cannot be cooled below the outside temperature.
- The A/C compressor is disabled when VENT is selected.
- The blower motor is on.
When OFF is selected:
- The air inlet blend door is at full vacuum, closing off outside air and allowing only recirculated air.
- The vent/register blend door is at no vacuum and the defrost, footwell and blend airflow doors are at no vacuum, closing off the passages to the driver, passenger and center registers.
- The blower motor and the A/C compressor are off.
When PANEL/FLOOR is selected:
- The air inlet blend door is set at no vacuum, blocking the recirculation passage and allowing outside air.
- The footwell blend door is in the full vacuum position, and the panel airflow door is in the full vacuum position allowing airflow to blend between the panel vents and the footwell ducts.
- The defrost airflow door is at full vacuum, closing off airflow to the windshield defroster hose nozzle and directing airflow to the heater outlet footwell duct.
- The A/C compressor is enabled when PANEL/FLOOR is selected.
- The blower motor is on.
When FLOOR is selected:
- The air inlet blend door is in the no vacuum position, blocking recirculation air and allowing outside air.
- The footwell airflow door is at the full vacuum position, opening the door and allowing airflow through the footwell ducts.
- The defrost airflow door and the vent/register blend door are in the no vacuum position, closing off air-flow to the windshield defroster hose nozzles and driver, passenger and center registers.
- The temperature control can be positioned to mix air flowing through and around the heater core to achieve the selected temperature level.
- The A/C compressor is disabled when FLOOR is selected.
- The blower motor is on.
When FLOOR/DEFROST is selected:
- The air inlet blend door is in the no vacuum position blocking recirculation air and allowing outside air.
- The footwell blend door is at full vacuum allowing air to flow through the footwell ducts.
- The defrost blend door is in the no vacuum position, allowing airflow to both the windshield defroster hose nozzle and side window demister hose nozzle ducts.
- The vent/register blend door is in the no vacuum position.
- The A/C compressor is enabled when FLOOR/DEFROST is selected to dehumidify the air and reduce windshield fogging.
- The blower motor is on.
When DEFROST is selected:
- The air inlet blend door is in the no vacuum position, allowing outside air.
- The defrost blend door is at no vacuum, directing the airflow to the windshield through the defroster ducts and the side windows through the demister ducts.
- The panel airflow door and the footwell airflow door are in the no vacuum position so that most of the incoming air is directed to the windshield defroster hose nozzle. There is also airflow to the side window demister and hose.
- The temperature control knob setting will determine the amount of air that is directed through the heater core and the amount that bypasses the heater core.
- The A/C compressor is enabled when DEFROST is selected to dehumidify the air and reduce windshield fogging.
- The blower motor is on.
Vacuum Schematic
Function Selector Switch Vacuum Connector
Function Selector Switch Vacuum Application Chart
NOTE: A leak in the vacuum control circuits will send all airflow to the defroster outlets. This condition may occur during acceleration indicating a slow leak, exist at all times indicating a large leak, or it may exist only when specific functions are selected indicating a leak in that portion of the circuit.
AIR DISTRIBUTION
There are two sources of air available to the air distribution system:
- outside air
- recirculated air
Air distribution within the vehicle is determined by the function selector switch position. Air flow control doors are used to direct air flow within the A/C evaporator housing (if equipped) and heater. Vacuum control motors are used to position these air flow control doors. See CLIMATE CONTROL SYSTEM for description and operation of each of the system functions.
The air distribution system is designed to provide air flow from the defrost nozzle when no vacuum is applied to any of the vacuum control motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak.
Air enters the passenger compartment from the:
- instrument panel register
- heater outlet floor duct
- windshield defroster hose nozzle
- side window demisters
- rear footwell duct
Passenger compartment air is exhausted from the vehicle through open windows or through the air extractors located in the rear of the vehicle.
CONTROL COMPONENTS
Manual A/C
The manual climate control system heats or cools the vehicle interior depending on the position of the function selector switch and the temperature selected. The position of the function selector switch determines heating or cooling and air distribution. The temperature control setting determines air temperature.
The manual climate control system components include:
- blower motor switch resistor
- vacuum degas bottle tank
- climate control assembly
- blower motor relay
- A/C compressor clutch relay
- footwell vent vacuum control motor
- defrost vacuum control motor
- panel vent vacuum control motor outside air inlet vacuum control motor
- temperature blend door control cable
Control System Inputs
Climate Control Assembly
1. Temperature control switch
2. Function selector switch
3. Blower motor switch
The climate control assembly has three system controls:
- The A/C heater function selector switch combines a vacuum selector valve with two electrical switches to supply battery positive voltage (B+) to the A/C clutch circuit and the blower motor control circuit.
- The temperature selection is accomplished through cable-controlled positioning of the temperature blend door located in the heater core housing.
- The blower motor switch controls the blower motor speed by adding or bypassing resistors in the heater blower motor switch resistor.
Control System Outputs
Blower Motor Switch Resistor
The four-speed operation of the blower motor is achieved through the blower motor switch resistor and contains a thermal limiter which is used as a temperature protecting fuse. The assembly is located on the passenger-side on the evaporator core housing behind the glove compartment.
Blower Motor Relay
The blower motor relay supplies voltage to the blower motor and is activated when the key is ON and the function selector switch is in any position besides OFF. The blower motor relay is located under the instrument panel next to the steering column.
A/C Compressor Clutch Relay
The A/C compressor clutch relay supplies voltage to the A/C compressor clutch and is located in the battery junction box (BJB). The power control module (PCM ) can interrupt the A/C compressor operation through the A/C compressor clutch relay under the following conditions:
- during engine start-up
- wide open throttle (WOT)
- low engine idle conditions
- excessively high engine temperatures